German laid-open application (DE-OS) No. 30 23 415.2 discloses an installation of that kind in which the moulds are arranged on a turntable which is moved with a stepwise motion in a circulatory path. While the female mould portions are rigidly supported on the turntable, the mandrels are fixed thereto pivotably and displaceably along the working axes. The actuating means for producing the displacement of the mandrels are mounted on working stations associated with the turntable. These working stations follow the material feed station in the direction of rotation of the turntable. When the turntable is in a stationary condition, the actuating means act on a respective mandrel to initiate the pressing operation or to produce the withdrawal movement of the mandrel.
In regard to pressing processes of the kind used herein, as the plastic material is introduced into the mould in an open condition, at least that period of time which is required for the mould to be closed or for the pressing force to be applied elapses before the actual deformation operation by pressing begins. If the plastic material is introduced into the female mould portion in a form in which it is plasticised by virture of heat, and if the female mould portion is cooled, as in an industrial use, then the period of time which elapses between the introduction of the material and the pressing operation may have a detrimental effect on the quality and/or the appearance of the pressed article.
In an installation of the specified kind, those considerations are relevant because the material feed nozzle and the female mould portion must occupy a common axial position for the operation of introducing the plastic material.
The residence time of the plastic material in the non-pressed condition in the female mould portion therefore necessarily includes that period of time that the turntable requires to transport the female mould portion from the station which gives the above-mentioned axial position, to the station for initiating the pressing operation.